This invention relates to control mechanisms for drive trains of vehicles and more particularly relates to manual override systems for electronically controlled automatic transmissions in military vehicles such as tanks.
Presently, the U.S. Army utilizes the M1 or M1A1 tank, which has an automatic transmission electrically controlled by a transmission shift selector located in the driver's compartment and monitored by the ECU (Electronic Control Unit). Solenoid operated valves on the transmission respond to signals from the transmission shift selector to control hydraulic circuitry within the transmission, thereby effecting engagement or disengagement between clutches and gears of the transmission. It is contemplated that power to the shift selector or to the solenoid operated valves can be interrupted because of battle damage to the tank or failures such as loose electrical connections or short circuits. An existing mechanical override for automatic transmission has a plunger under an access plate on the tank for the automatic transmission. A disadvantage of the existing manual override is that the plunger can place the transmission only in drive, and can not place the transmission in reverse. To use the override plunger, a soldier must exit the tank, unbolt the access plate, remove the plate, and use a three-foot bar to push the plunger into the override position. This procedure is time consuming and exposes the soldier to enemy fire. In a battle scenario, there is a significant risk that the tank will be destroyed or its crew killed by enemy fire before the tank transmission can be placed in its mechanical override mode. Further, the tank engine cannot be shut down during this procedure and the access plate is located between engine exhaust ports from which blows an extremely hot stream of exhaust gas. Consequently, removing the access plate and actuating the override is inherently inconvenient and even dangerous for the soldier doing it.
We propose a manual or mechanical override mechanism for shifting the automatic transmission of a tank, the mechanism being operable from within the tank, thereby avoiding the problems mentioned above. Our mechanical shifting mechanism is controlled by a push-pull cable running from a gear shift lever in the driver's compartment of the tank. The cable actuates a series of mechanical links and gear train members and ultimately turns a specifically lobed cam shaft. The turning cam shaft moves selected actuator blocks, thus causing activation of solenoid valves which accomplish the range selection of the transmission. Our mechanical shifting mechanism is designed to be installed or existing automatic transmissions in M1 and M1A1 tanks without a major overhaul on their drive trains. The individual elements of the shifting mechanism are easily removed from the mechanism or from the tank to facilitate their installation or repair.